This invention relates to an automatic diaphragm aperture control photographic camera for automatically controlling the diaphragm aperture to an optimum aperture value by interrupting the stop-down operation of the diaphragm according to the output of the light from a photographic object, which light has been transmitted through an objective lens and the diaphragm aperture, as the diaphragm aperture is being stopped down from its fully open condition.
An exposure control device for a photographic camera has been heretofore known wherein a light measuring device measures the light from a photographic object, in which light has been transmitted through an objective lens and a diaphragm aperture for effecting a stop-down operation, with the diaphragm aperture being stopped sown from its fully open condition in association with the shutter releasing operation. Then, an interlocking pin which cooperates with this stop-down operation is locked by means of a locking member according to a light measuring output, thereby controlling the diaphragm aperture to an optimum aperture value corresponding to the shutter speed which has been selected beforehand, commensurate with the brightness of the photographic object.
However, such exposure control device presents disadvantages which will be described hereinafter. For example, the diaphragm aperture providded for the objective lens is governed by the movement of diaphragm blades which are operated by means of a diaphragm ring. This is so even if diaphragm graduations are provided at an equal spacing, and the extent of the movement of the diaphragm blades required for stopping down the diaphragm aperture by a one step operation becomes less as the diaphragm aperture becomes smaller. This in turn leads to difficulties in controlling the moving extent of the interlocking pin by means of the aforesaid locking member, when the diaphragm aperture has been stopped down to some extent.